Canyons are inherently risky. Flash floods occur without notice on sunny days. Technical skills & surrounding topography knowledge required yet does not eliminate risk.
Sticky, Prickly, Tumbly...
Sotol Canyon is the first side canyon (on your left) as you enter Marble Canyon. It cuts across the old access road that leads up to the Marble Quarry. For all practical purposes, it well could be avoided; it is overgrown, filled with loose rock over unstable dirt... and, it is way steep. The way steep part might be its saving grace for some hikers.
As the leading leg of a loop, it can provide an interesting bit of training. Moving very slowly and with great caution (and you better be doing both) your heart rate may still be ranging into the upper cardio levels. As you work your way up and around the various obstacles you will score a great workout. While it is a shortcut over to the "A" trail, it does not allow you to get over there fast. This is a slow route.
It does wind up and over to connect with that other trail. If you desire a simple two hour loop and do not feel like pushing the pace, just making your way around this narrow canyon will get the job done.
You have the option of making your way along the bottom of the rocky cut, often overgrown... or, try to follow one of the numerous game trails that work their way around and up.
The canyon splits and spans out to a broad basin after your climb through the lower cliffs. The far left branch remains the steepest. The right side provides an easier approach. Eventually, you will want to move to the far right of the drainage where you will encounter Trail 119 ("A" Trail) as it passes some old excavations. At this point you are about 1.1 mile from the trail head and 700' up from that level.
You could head down, or consider going higher and looping around and down the Quarry Canyon, looping you back to the Marble Quarry.
I did it once... you might as well, too!
Note: you cross private property making your way up and into Marble Canyon. Be quiet and respectful of this privilege.
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.